Expulsion lightning arrester



April a8, 1947. R. R. PITTMAN EXPULSION LIGHTNING ARRESTER Filed Sept. 28, 1943 2 Sheets-Sheei, l

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EXPULS ION LIGHTNING ARRESTER Filed Sept. 28, 1943 2 Sheets-Sheet, 2

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z i Initiating Electrodes V Fig. 6 a-A position of orc /l2 when initiated bc- Intermediate positions of orc LIB d- A position of orc Arcing 2O t when extinguished Electrodes e4- Direction of gos discharge iv i 7i.

INVENTOR Patented Apr. 8, 1947 UNITED STATES PATENT OFFICE EXPULSION LIGHTNING ARRESTER Ralph R. Pittman, Pine Bluff, Ark. Application September 28, 1943, Serial No. 504,201

8 Claims.

This invention relates generally to lightning protective devices, and particularly to the type of lightning arresters in which arcing gaps are embodied for the purpose of limiting the Voltage of a connected conductor to a predetermined magnitude, and in which an arc following sparkover of the gaps is quickly extinguished by eX- pulsion action.

The present invention is an improvement on the construction described in my pending application Serial No. 409,009, iiled August 30, 1941, which application matured into Patent No. 2,- 336,420, dated December 7, 1943 and has for one of its objects the provision of means responsive to the occurrence of an initial or primary arc for extinguishing the arc in the initial path concurrently with the establishment of a secondary arc, and for extinguishing the secondary arc.

More specifically, it is an object of the present invention to provide an improved construction in a voltage limiting and arc extinguishing device in which sparkover always occurs over a predetermined arc path along a transversely extending line of abutment between the upper end of a tapered plug of insulating material and a tubular insulator in which the plug is tightly fitted, and in which the arc which may attend sparkover is elongated within an annular space between the inner surface of the insulator and the outer surface of the tapered plug by the gaseous arc products which pass acrossthe arc as they move toward a vented end of the insulator, the annular space increasing in cross-sectional area along the taper toward the vented end of the insulator to facilitate the elongation of the arc.

In the construction illustrated in the abovementioned application, sparkover always occurs between electrodes located at the respective ends of the tapered portion of the plug. In principle, the present invention is distinguished in one respect by a construction in which sparkover al ways occurs along the line of abutment of that end of the tapered portion which lls the bore of the containing insulator. The latter construction has been found to operate to move the arc more quickly from the sparkover path, probably because the arc space becomes wider in a direction normal to the sparkover path, instead of parallel thereto, as in the construction described in the above-identified application.

Another object of the presentinvention is the provision of a construction embodying a pair of initiating electrodes and a pair of arcing electrodes in which the arc is quickly moved from occurring at or near current zero.

the initial path to a path between the arcing electrodes where extinguishment occurs. Expulsion devices in general will not complete arc extinguishment in less than 1/2 cycle of an alternating current system, existinguishment usually It is well known that considerable erosion and electrode burning takes place in the duration of l cycle, particularly when interrupting currents of the order of G-5000 amperes R. M. S., and it is very desirable that such burning and erosion take place at some location other than the initial sparkover path. Otherwise, the initial path, being necessarily short to provide low initial sparkover, may quickly become so unrestricted because of erosion that extinguishment following repeated operations may not be accomplished. The provision of arcing electrodes, and means for quick transfer of the arc current thereto, i. e., in considerably lessV than 1/2 cycle, makes possible a simple and economical construction in which the critical elements of the device cannot be damaged by erosion.

With these and other objects in view which will appear from the description, my invention resides in the novel form, combination and construction of the parts of the device, and the scope of the invention will be indicated by the appended claims.

In the drawing: Fig. 1 is a side elevational View of the device, shown in section; Fig, 2 is a front elevational view, shown partly in section; Figs. 3, 4 and 5 are respectively sections taken along the lines 3 3, 4 4, and 5--5 of Fig. 2; Fig, 6 is a fragmentary development of the inner surface of the arc chamber, showing progressive positions taken by an imaginary arc from its inception to its extinguishment; and Fig. 'I is a fragmentary development taken along the line 1-1 of Fig. 6.

Referring in detail to the drawing, a hollow tubular insulator l0 is provided at its upper end with a cap 25 and an upper terminal 26, the conducting rivet 24 extending laterally through the upper end of the insulator I0 and fastening the other elements thereto.

An inner element or plug of insulating material Il extends longitudinally within the bore of the tubular insulator I0. The element Il is formed with an upper portion l2 which is tted tightly into andcompletely lls an upper portion of the insulator .Iman intermediate' portion I3 which;

merges with and tapersdownwardly from the diameter of the insulator I0 to a diameter less than that of the insulator, and a lower portion I4 which extends coaxially from the smaller diameter of the tapered portion I3 toward the lower and open end of the insulator` I0. The lower portion I4 of the element II partly fills the bore of the insulator I0, being provided with opposed attened sides between which extend the circumferentially spaced outwardly extending portions I5, the latter longitudinally abutting the inner surface of theinsulator I U andholding the plug II in coaxial position with respect toV the lower portion of the insulator I 0.

Preferably both the insulator lil and the 'plug II are constructed-from material which evolves gas which is conducting at or near atmospheric pressure when an arc occurs between these elements. Hard fiber is a satisfactory material.

The above-described construction is such that a circumferentially extending line of abutment is provided at the upper end of the tapered portion I3 with the inner surface of the insulator I0, and the passageways I'I provide venting in such a manner that there is provided an arc space or chamber I6 which is vented to the outside of the insulator I from the line of abutment of the plug II therewith.

A pair of conducting, diametrically spaced initiating electrodes I8 and I9 respectively are mounted along the line'of abutment of the. upper end of the tapered portion I3 with the inner surface of the insulator I0, and a pair of conducting, diametrically and longitudinally spaced arcing electrodes 20' and 2l respectively are mounted below the initiating electrodes and nearer to the open end of the insulator I0. A conducting member 22, located Within the element kI I, electrically connects the first initiating electrode I8. to the rst arcing electrode 20, and a conducting meniber 23, which is conveniently in the form of a sleeve embracing the insulator I0, electrically connects the second initiating electrode I9 to the second arcing electrode 2I. A lower terminal' 2l may be connected at any convenient point to the sleeve 23, and in the embodiment illustrated is clampedbetween the head of the cap screw forming the second arcingelectrode 2l andthe sleeve 23.

The weakest Velectrical path throughthe device is from the upper terminal 26, thence along the rivet 24, thence along-the conducting member 22 to the first initiating electrode i8, thence along the curved line of abutment between the plug II andthe insulator I0 tothe second initiating electrode I9, thencethroughthe conducting member 23to the-lower terminalY 2'I. Sparkover always occurs along the line ci abutment in response to occurrence ofa predetermined diierence of potential between the respective terminals of the device.

Reference is made to Figs. 6 and 7 for the purpose of describing an imaginary operation of the device when a primary arc follows sparkover along, the initial path between the initiating electiodes I8 andv I3. T-he gas attending the arc is initially highly conducting, and as it moves downwardly along the continuously less restricted space formed by the tapered portion; the primary arc is moved from the position a to the intermediate position b. Whether the arc will remain in position J-until extinguishment occurs is determined, among; things, lby rthe l magnitude of the folloivvcurrentfloiving in the arc. Small currents,

for example,- currentsof less thana few hundredv amperes, are quickly extinguished in the position b when the. device is built to certain definite specifications to be later stated. If the arc is not interrupted in the position b, the continued evoluticn of gas may move the arc to the position c, that is, between the arcing electrodes 20 and 2I, and electrically in shunt with the path between the initiating electrodes where the arc originated. Again the magnitude of the current becomes a consideration affecting extinguisln'nent. and it may be necessary that the arc be further elongated as it is driven at.. the arc choppers l5 before extinguishment occurs, indice by the line d.

Since the conductivity of the gas attending the arc is a function of the pressure, and since the pressure approaches atmospheric at the open end of the device, the arc requires proportionately greater elongation to cause extinguishment. This elongation is believed ossible because restrike across the initial path is prevented by the much higher pressure along the initial path, although the latter is relatively much shorter.

If the device is constructed with regard to the voltage gradients along the possible arc paths, elongation of the arc to extinguishrnent is readily accomplished without restrike along the initial path. As an example of a practical construction, in which hard fiber was employed the material of the insulating elements, the following dimensions have been found effective in the accomplishnient oi the objects` of the invention, for interrupting 3000 volt, 60 cycle The diameter of the tubular .insulator is 34; the taper from 3,3 to 5/8" in 11/2" length; sparkover path about l long between the electrodes at the top of the tapered portion; the first arcing electrode at the lower end of the tapered portion; the second arcing electrode at a distance about 2% below and diametrically opposite the iirst arcing electrode; and the total cross-sectional area between the lower portion I6 of the plug and the inner surface of the insulator about 0.10 square inch. With ,he construction as specified, arc extinguishment occurs along the path a with currents from zero to about amperes; along the path b from about 100 to about 600 amperes; along the path c from about 600 to 1000 amperes; and along the path d for currents exceeding about 1000 amperes.

As a consideration in the operation of the device, it is noted that arc transfer takes place with great rapidity, the entire sequence to extinguishment requiring a maximum of 0.0083 second, or 1/2 cycle of a 60 cycle per second system. Arc transfer may occur so quickly from the initial path that evidence of pitting or burningr of the initiating electrodes may be either not at all visible or barely discernable, while the marking appearing on the arcing electrodes is quite apparent. Absence of burning at the initiating electrodes, and absence of erosion of the insulating material adjacent thereto, is regarded as an unexpected advantage of the invention.

For certain practical applications of the device, for example, when interrupting follow currents oi less than about 1000 amperes, the lower untapered portion of the plug and the lower arcing electrode may not be required. For such applications, it is desirable to provide the arcing electrode near the lower end of the tapering portion to avoid erosion ofthe insulating material surrounding at least one of the initiating electrodes, as otherwise the initial path becomes so eroded after a few operations when interrupting currents at the upper end of the current range stated that the restriction may not be such as to cause extinguishment along the initial sparkover path.

Irrespective of the practical application, it will be apparent that the insulating members of the device must be so coordinated that sparkover will always occur along the line of abutment between the initiating electrodes. It will also be clear that dimensions other than those stated above may be desirable for devices used on circuits diiering as to electrical characteristics from those stated in the example.

The entire foregoing description of my invention is intended as illustrative rather than limiting.

I claim as my invention:

l. A voltage limiting and arc extinguishing device comprising a hollow tubular insulator open at the lower end thereof, an element of insulating material extending coaxially within said tubular insulator, said element of insulating material being formed with an upper portion which closes the upper end oi said insulator, a lower portion which partly lills the lower portion of said insulator and which longitudinally abuts at circumferentially spaced points the inner surface thereof so as to support said element in coaxial relationship with said insulator and to provide a plurality of circumferentialiy spaced passage Ways between the lower end of said upper por tion of said element and the open end of said insulator, a tapered intermediate portion of said element the upper end of which abuts along a curved line the inner surface of said tubular in sulator, said tapered portion extending longitudinally within said insulator and joining the upper and lower portions of said element, and structural means for causing sparkover to occur transversely along the curved line of abutment of the upper end of said tapered portion with the inner suriace of said tubular insulator, said structural means including normally insulated conducting electrodes so related that the weak est electrical path through the device is therebetween, said electrodes being mounted in spaced relationship at the elevation of said line of abutment.

2. An expulsion lightning arrester comprising a tubular insulator open at the lower end, a plug of insulating material having an upper portion thereof tightly fitted into said insulator, a downwardly tapering portion merging with said upper portion to provide a circumferential line of abutment between said plug and the inner surface of said tubular insulator, and a lower portion extending downwardly within said insulator from the smaller end of said tapered portion toward the open end of said insulator, said lower portion partly `Filling the bore of said insulator to pron vide a communicating passageway between the open end of said insulator and said line of abutment, structural means for causing sparkover to occur along said line of abutment, said structural means including circumierentially spaced, normally insulated conducting initiating electrodes mounted along said line of abutment and arranged to provide therebetween the weakest electrical path through the arrester, at least one normally insulated conducting arcing electrode mounted at the inner surface of said passageway between said line of abutment and the open end of said insulator, and conducting means connecting said arcing electrode to only one of said initiating electrodes.

3. An expulsion lightning arrester comprising a tubular insulator of a material which evolves conducting gas in the presence of an arc at atmospheric pressure, structural means for causing sparkover to occur within said insulator, said structural means including a pair of normally insulated conducting electrodes mounted in circumferentially spaced relation along the inner surface of said insulator, said initiating electrodes being so related that the weakest electrical path through the arrester is therebetween for initiating a primary arc over said path within said insulator and causing evolution of conducting gas from said material, a pair of normally insulated conducting arcing electrodes mounted along the inner surface of said insulator in circumferentially spaced relationship to one another and in longitudinally spaced relationship to said initiating electrodes, means for guiding said conducting gas over an arc path between said arcing electrodes, and means for establishing in shunt relation with said primary arc a secondary arc concurrently with extinguishment of said primary arc, said last-named means including a conducting member connecting one initiating electrode to one arcing electrode and another conducting member connecting the other initiating electrode to the other arcing electrode, the respective conducting members being isolated from both the primary and secondary arc paths.

e. A voltage limiting and arc extinguishing device comprising nested elements of insulating material constituting a restricted arcing chamber therebetween closed at one end and open at the other end, means supporting in spaced relationship at least four conducting electrodes arranged to form parte of the conning wail or said. arcing chamber, said 'four conducting electrodes including two normally insulated circumferentially spaced initiating electrodes located at the closed end of said arcing chamber and so related that the weakest electrical path through the device includes the path within said chamber between said initiating electrodes, and two normally insulated arcing electrodes located between the respective ends of said arcing chamber and spaced a greater distance apart within said chamber than said initiating electrodes, and conducting means separately connecting respectively one of said initiating electrodes to one of Said arcing electrodes and the other or lsaid initiating electrodes to the other ci said arcing electrodes, said conducting means being isolated from both one another and from said arcing chamber.

A voltage limiting and. arc extinguishing device comprising nested elements of insulating material constituting a restricted arcing chamber therebetween closed at one end and open at the other end, means supporting in spaced relar tionship at least four conducting electrodes arranged to form parts of the confining walls of said arcing chamber, said four conducting elec trodes including two normally insulated circumerentially spaced initiating electrodes located at the closed end of said arcing chamber and two normally insulated arcing electrodes located between the respective ends of said arcing chamber and spaced a greater distance apart within said chamber than said initiating electrodes, and conducting means separately connecting respec tively one of said initiating electrodes to one or said arcing electrodes and the other of said in itiating electrodes to the other or said arcing electrode's, said conducting means being isolated from both one another and from said arcing chamber, the conducting elements of the device being so related that sparlrover always occurs alongr the circumferential path between said initiating electrodes.

6. A voltage limiting and arc extinguishingvdevice comprising tubular insulator open at the lower end, a. plug of insulating material having an upper portion tlrweof tightly fitted into said insulator' coaxial relationship therewith, a downwardly tapering portion merging coaxially with said upper portion to provide a curved line of abutment between `said plug and the inner surface of said insulator, and a lower portion extending coaxially and downwardly within said insulator from the smaller end of said tapered portion the open end oi said insulator, said lower por -un partly :filling the bore of said insulator to provide aradlally extending opening which longitudinally extends from the open end of said insulator to said line of abutment, structural means for causing sparkover to occur along said line oi abutine said Structural means including transversely spaced normally insulated conducting first and second initiating electrodes mounted along line o abutment andso relater as to provide therebetween the weakest electrical path. or" greatest restriction through the device, and transversely spaced normally insulated coridu g and second arcing electrodes mountsbelow initiating electrodes and forming a part of the confining walls of said opening, conducting means connecting the rst initiating electrode to the ilrst arcinT electrode, and conduciirff means connecting the second initiating eli to the second arcing electroie.

'7. volta Je limiting and arc extinguishing denested elements of insulating tituting a rest icted arcing chamone end and open at the other end, ne including a hollow tubular insun the ad. an inner plug oi inerial fitted said insulator, said i upper portion of subi de di ieter of said insulator, ermediate portion which tapers longituy from a curved line of abutment of said upper portion with the inner surface of said insulator to a diameter less than that of said inr, and a lo\ portion which extends longi- .lly from the smaller diameter of said tin toward the open end of said insulator, said lower portion partly filling the bore tubularinsulatoi1 and longitudinally abute' ierentially spaced points the inner "f as to transversely support 'said d to provide a plurality of downg, curnierentially spaced pas- .een the lower and smaller end of said tapered portion and the open end of said stantially tl.e

insulator, means supporting in spaced relationship at least four conducting electrodes arranged to form parts of the confining walls of said arcing chamber, said four conducting electrodes including two normally insulated spaced initiating electrodes located at the closed end of said arcing chamber and s0 related that the weakest electrical path through the device includes the path within the chamber between said initiating electrodes, and two normally insulated arcing electrodes located between the respective ends of said arcing chamber and Spaced a greater distance apart within said chamber than said initiating electrodes, and conducting means separately connecting respectively one oi said initiating electrodes to one of said arcing electrodes and the other of said initiating electrodes to the other of said arcing electrodes, said conducting means being isolated from one another and said arcing chamber.

8. An expulsion lightning arrester comprising a tubular insulator open at the lower end, a plug of insulating material having an upper portion thereof tightly tted into said insulator and a downv-.fardly tapering portion merging with said upper portion to provide a circumferential line ol abutment between said plug and partly filling the bore of said insulator to provide an arcing chamber between the open end of said insulator and said line of abutment and between the outer surface of said tapering portion the inner surface said insulator, structural means for causing sparkover to occur along said line oi" abutment, said structural means including circumferentially spaced, normally insulated conducting initiating electrodes mounted along said line 0i abutment and arranged to provide tl'ierebetwecn the weakest electrical path through the arrester, at least one normally insulated co ducting arcing electrode mounted at the inner surface of said arcing chamber between said line of abutment and the open end of said insulator, and conducting means connecting said arcing electrode to only one of said initiating electrodes.

RALPH PITTMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

